如何在指定列表中找到第一个值？

my_list = [1, 2, 3, 4, 5]
first_value = my_list[0]

class Node:
    def __init__(self, value):
        self.value = value
        self.next = None

# 创建链表
head = Node(1)
second = Node(2)
third = Node(3)
head.next = second
second.next = third

# 获取第一个值
first_value = head.value

my_dict = {'a': 1, 'b': 2, 'c': 3}
first_key = next(iter(my_dict.keys()))
first_value = my_dict[first_key]

my_set = {1, 2, 3, 4, 5}
first_value = list(my_set)[0]  # 转换为列表后获取第一个值
# 或者
for value in my_set:
    first_value = value
    break